Certains forms of cancer are believed to be less common when the diet contains "dietary fiber". We propose to examine the physico-chemical properties of lignins in preparations partially or fully separated from plant fiber, and thereby to provide a basis for hypotheses on the role of this constituent in the diet in relation to carcinogenesis. The binding of several carcinogens and co-carcinogens to these lignins will be studied. The main emphasis will be on nitrosamines and other nitrosocompounds and bile salts. Lignin may also influence carcinogenesis through its oxidation-reduction properties, and through reaction with nitrates. It can also bind metal ions and other significant substances in the diet. The study will thus illustrate the effect of lignin on the bioavailability of a variety of substances implicated in carcinogenesis.